Objective

In this article, I am going to show, how we could apply LINQ to query non-IEnumerable<T> Collections.

I have created a class for my explanation purpose. Student class is having details of students.

 Student.cs

    1 using System;

    2 using System.Collections.Generic;

    3 using System.Linq;

    4 using System.Text;

    5 

    6 namespace LINQtoOBJECT1

    7 {

    8      public  class Student

    9     {

   10 

   11          public int RollNumber { get; set; }

   12          public string Name { get; set; }

   13          public int Section { get; set; }

   14          public int HostelNumber { get; set; }

   15     }

   16 }

   17 

 

To create ArrayList of Student, I am creating a static function. This static function will return ArraList of student.

Function to return ArrayList of students.

    1  public static ArrayList   GetStudentAsArrayList()

    2         {

    3 

    4             ArrayList  students = new ArrayList

    5             {

    6                 new Student() { RollNumber = 1,Name =“Alex “ , Section =  1 ,HostelNumber=1 },

    7                 new Student() { RollNumber = 2,Name =“Jonty “ , Section = 2 ,HostelNumber=2 },

    8                 new Student() { RollNumber = 3,Name =“Samba “ , Section = 3 ,HostelNumber=1 },

    9                 new Student() { RollNumber = 4,Name =“Donald “ , Section = 3 ,HostelNumber=2 },

   10                 new Student() { RollNumber = 5,Name =“Kristen “ , Section = 2 ,HostelNumber=1 },

   11                 new Student() { RollNumber = 6,Name =“Mark “ , Section = 1 ,HostelNumber=2},

   12                 new Student() { RollNumber = 7,Name =“Gibbs “ , Section = 1 ,HostelNumber=1 },

   13                 new Student() { RollNumber = 8,Name =“Peterson “ , Section = 2 ,HostelNumber=2 },

   14                 new Student() { RollNumber = 9,Name =“collingwood “ , Section = 3 ,HostelNumber=1 },

   15                 new Student() { RollNumber = 10,Name =“Brian “ , Section = 3 ,HostelNumber=2 }

   16 

   17             };

   18 

   19             return students;

   20 

   21         }

 Now when I tried to query the returned ArrayList using LINQ, I got compile time error. Because ArrayList does not implement interface IQueryable and it is not IEnumerable<T> collection.

 Below code gave a compile time error

    1 ArrayList lstStudents = GetStudentAsArrayList();

    2             var res = from  r in lstStudents select r;

Error is as below,


Above error cause because LINQ by default only query against IEnumerable<T> collections.

So , how to query an ArrayList? Here Range variable comes into action. If I modify the above query as below , I would be able to query LINQ against a non IEnumerable<T> collection.

    1 using System;

    2 using System.Collections.Generic;

    3 using System.Linq;

    4 using System.Text;

    5 using System.Collections;

    6 

    7 

    8 namespace LINQtoOBJECT1

    9 {

   10     class Program

   11     {

   12         static void Main(string[] args)

   13         {

   14 

   15 

   16             ArrayList lstStudents = GetStudentAsArrayList();

   17             var res = from  Student   r in lstStudents select r;

   18             foreach (Student s in res)

   19             {

   20                 Console.WriteLine(s.Name);

   21             }

   22 

   23            Console.ReadKey();

   24 

   25 

   26 

   27         }

I am using Student as range variable. And we will get output as below .In above code I am using Student the class in ArrayList as range variable.


Conclusion

In this article, I discussed how to query against non IEnumerable<T> collection. Thanks for reading.

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One thought on “LINQ to Object Part #4: Querying Non- IEnumerable collections

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